Method of compensating for boil-off alcohol in a flexible fueled vehicle without a PVC solenoid

Abstract

The present invention provides a method of controlling combustion parameters of an internal combustion engine without a PCV solenoid during a boil-off condition. The methodology detects a boil-off condition and implements one of two modes of boil-off compensation depending on the active status of an inferred alcohol content multiplier update system. The methodology also determines the nature of the air-flow through the internal combustion engine and determines the level of boil-off corruption present and the time when the corruption is complete. After the boil-off condition is determined to be complete, control of the combustion parameters are returned to a normal regime of a flexible fuel compensation system using the inferred alcohol content from the employed mode of boil-off compensation.

What is claimed is: 
     
       1. A method of controlling combustion parameters of an internal combustion engine in a flexible fueled vehicle without a PCV solenoid during an alcohol boil-off condition comprising: detecting a boil-off condition;   detecting an active/inactive status of an inferred alcohol content update system;   implementing a first mode of boil-off compensation if said inferred alcohol content update is active;   implementing a second mode of boil-off compensation if said inferred alcohol content update is inactive;   detecting a high/low nature of an airflow through said internal combustion engine;   setting said combustion parameters for compensating for boil-off corruption according to a first routine based on one of said first and second modes at high engine airflows;   setting said combustion parameters for compensating for boil-off corruption according to a second routine based on one of said first and second modes at low engine airflows;   detecting when said boil-off condition is complete; and   returning said control of said combustion parameters to an oxygen sensor feedback based flexible fuel compensation system according to one of said first and second modes of boil-off compensation after said boil-off condition is complete.   
     
     
       2. The method of claim 1 wherein said first mode of boil-off compensation further comprises: updating an inferred alcohol content value below a specified coolant temperature when said boil-off condition is detected;   holding said inferred alcohol content value at a current value when said specified coolant temperature is reached;   storing said inferred alcohol content value to a temporary storage location; and   updating said temporary storage location at high airflows to compensate said combustion parameters for alcohol boil-off corruption after a specified coolant temperature is reached.   
     
     
       3. The method of claim 2 wherein said specified coolant temperature defines a region where boil-off corruption does not occur. 
     
     
       4. The method of claim 1 wherein said second mode of boil-off compensation further comprises: holding an inferred alcohol content value at a current value when said boil-off condition is detected;   storing said inferred alcohol content value to a temporary storage location; and   updating said temporary storage location at high airflows after a specified coolant temperature is reached to compensate said combustion parameters for alcohol boil-off corruption.   
     
     
       5. The method of claim 4 wherein said specified coolant temperature defines a region where boil-off corruption cannot occur. 
     
     
       6. The method of claim 1 wherein said step of returning control of said engine operating parameters to said flexible fuel compensation system further comprises using said updated inferred alcohol content for fuel control if said methodology is operating in said first mode of boil-off compensation and basing said fuel control on said inferred alcohol content value from a previous update if said methodology is operating in said second mode of boil-off compensation. 
     
     
       7. The method of claim 1 wherein said step of detecting a boil-off condition further comprises: determining if a start coolant temperature of said internal combustion engine is greater than a known value;   determining if a start battery temperature of said vehicle is greater than said known value;   determining if the number of crankshaft revolutions counted before a start-to-run transfer is made in said vehicle is greater than a second known value; and   determining if a percent alcohol content of fuel during a drive of said vehicle is greater than a third known value.   
     
     
       8. The method of claim 1 wherein said step of determining when said boil-off condition is complete corresponds to a difference in boil-off corruption between said high and low airflows. 
     
     
       9. The method of claim 1 further comprising determining an amount of said boil-off corruption based on said nature of air-flow through said internal combustion engine. 
     
     
       10. The method of claim 1 further comprising updating said inferred alcohol content at high engine airflows to account for high levels of boil-off and updating and employing an additional fuel modifier to compensate for additional corruption experienced at low air-flows. 
     
     
       11. The method of claim 1 further comprising starting an exit timer and recognizing the expiration of said exit timer as the completion of said boil-off condition if a high airflow modifier is completely updated and if a low airflow modifier still indicates a low level of boil-off.